Small diameter evacuation head for VIG unit manufacture

ABSTRACT

A method of producing a vacuum insulated glass (VIG) unit comprising providing first and second substantially parallel glass panes, a plurality of pillars, and a peripheral seal between the first and second glass panes; providing an evacuation hole for evacuating a void through the evacuation hole to a pressure less than atmospheric pressure, wherein the first and second glass panes are tempered glass; covering the evacuation hole with an evacuation head, wherein the evacuation head is configured to have a substantially hermetic contact to a surface of the first glass pane, wherein a contact width of the evacuation head to the surface of the first glass pane is less than 50 mm; and evacuating the void through the evacuation head.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application of PCT/DK2016/050281,filed Aug. 22, 2016, which claims the benefit of DK Application No.PA201500487, filed Aug. 20, 2015, the entire contents of which areincorporated herein by reference.

BACKGROUND

This disclosure relates to a vacuum insulating glazing (VIG) unit. Inparticular, it relates to the vacuum evacuation head (also known as allmetal cup). And sealing of the evacuation tube with a heater inside theevacuation head.

Vacuum insulating glazing (VIG) units typically comprise two glass panesspaced by pillars, sealed at the periphery and having an evacuatedinterior void. The void is evacuated with an evacuation head through ahole in the pane to a pressure such as 1E-6 bar.

US2006175767 discloses a VIG unit and an evacuation head being 70 mm.The disclosure deals with a gasket to ensure a good seal. Paragraph[0061] does mention an evacuation head diameter of 50 mm to 100 mm.

US20120148795 deals with the sealing of the evacuation hole. Itdiscloses a prior art evacuation tube and evacuation head with a coilheater (FIG. 2a) which is used to melt the tube tip (also known as thetip off).

BRIEF SUMMARY

For decades there has been ongoing work with VIG gazing due to thepromising insulation value which enables great energy savings tobuildings. Production of VIG units however still has several drawbacksand lifetime challenges. It would be desirable to provide a bettercontact seal between the evacuation head and the glass pane. Further itwould be desirable to provide an enhanced evacuation tube seal by bettertemperature application and better tube tip off. Further it would bedesirable to provide a tempered glass VIG.

The disclosure relates to method, a VIG manufacture facility and a VIGunit. Favorable embodiments are defined in the dependent claims. Otherobjectives, features and advantages will appear from the followingdetailed disclosure. In particular, the disclosure relates to the belowspecific aspects and embodiments.

In a first aspect and embodiment there is disclosed a method ofproducing a vacuum insulated glazing (VIG) unit comprising: providingfirst and second substantially parallel panes 1,2, a plurality ofpillars 4 and a peripheral seal 3 provided between the first and secondpanes 1,2, where in the first pane 1 there is provided an evacuationhole 5 for evacuating a void V through the evacuation hole 5 to apressure less than atmospheric pressure; wherein the panes 1,2 aretempered glass; on a glass pane face 1 a, covering the evacuation hole 5with an evacuation head 8, the evacuation head 8 adapted to have asubstantially hermetic contact to the glass pane face 1 a; wherein theevacuation head 8 contact width D to the pane face 1 a is less than 50mm, preferably less than 45 mm; and evacuating the void V through theevacuation head 8.

In a second embodiment of the first embodiment of the first aspect thereis disclosed a method of producing a VIG unit according to the previousembodiment, wherein the evacuation head 8 is adapted to reduce thetemperature difference in the VIG body beneath the evacuation head 8from the temperature in the surrounding VIG body.

In a third embodiment of the first embodiment of the first aspect thereis disclosed a method of producing a VIG unit according to any previousembodiment, wherein the VIG unit is in an oven and the void V isevacuated in the oven.

In a fourth embodiment of the first embodiment of the first aspect thereis disclosed a method of producing a VIG unit according to any previousembodiment, wherein the VIG body production in an oven includes heatingthe VIG unit in the oven and in all steps keeping the temperature belowan annealing temperature, which detrimentally affects the temperedglass, such as keeping the temperature below 400° C.

In a fifth embodiment of the first embodiment of the first aspect thereis disclosed a method of producing a VIG unit according to any previousembodiment, wherein the evacuating of the void V is done at 150° C. ormore, preferably at 300° C. or more.

In a sixth embodiment of the first embodiment of the first aspect thereis disclosed a method of producing a VIG unit according to any previousembodiment, wherein the temperature of the oven is between 150° C. and400° C., preferably between 300° C. and 400° C.

In a seventh embodiment of the first embodiment of the first aspectthere is disclosed a method of producing a VIG unit according to anyprevious embodiment, wherein the evacuating of the void V is done in theheated oven after substantially soldering the peripheral seal 3.

In an eighth embodiment of the first embodiment of the first aspectthere is disclosed a method of producing a VIG unit according to anyprevious embodiment, wherein the peripheral seal 3 is substantiallysoldered in the heated oven and subsequently the evacuating of the voidV is initiated.

In a ninth embodiment of the first embodiment of the first aspect thereis disclosed a method of producing a VIG unit according to any previousembodiment, wherein an evacuation tube tip 6 b is sealed off by heatprovided by a heat element 9 in the evacuating head 8 chamber 10.

In a tenth embodiment of the first embodiment of the first aspect thereis disclosed a method of producing a VIG unit according to any previousembodiment, wherein the evacuation head 8 is substantially circular andthe contact width D is a diameter D.

In an eleventh embodiment of the first embodiment of the first aspectthere is disclosed a method of producing a VIG unit according to anyprevious embodiment, wherein the pillars 4 are spaced a distance S andwherein the evacuation head 8 contact width D is equal or less thanpillar 4 distance S.

In a twelfth embodiment of the first embodiment of the first aspectthere is disclosed a method of producing a VIG unit according to anyprevious embodiment, wherein the evacuation head 8 has a ceramic heatingelement 9, and the method comprises: heating the ceramic heating element9 and sealing off the tip 6 b of an evacuation tube 6.

In a thirteenth embodiment of the first embodiment of the first aspectthere is disclosed a method of producing a VIG unit according to anyprevious embodiment, comprising: heating the ceramic heating element 9to a first temperature to provide a more uniform VIG body temperature T2beneath the evacuation head 8, and heating the ceramic heating elementto a second temperature to tip off the tube 6 b.

In a fourteenth embodiment of the first embodiment of the first aspectthere is disclosed a method of producing a VIG unit according to anyprevious embodiment, wherein the evacuation tube 6 is an evacuation cap18 comprising an evacuation port 20 and a solder glass ring 19 arrangedaround the evacuation port 20.

In a first embodiment of a second aspect there is disclosed a vacuuminsulated glazing (VIG) unit manufacture facility comprising an ovenwith a compartment adapted for heating a VIG unit, the oven comprisingan evacuation head 8 in fluid communication with at least one vacuumpump, wherein the evacuation head 8 contact width D to the VIG is lessthan 50 mm, preferably less than 45 mm.

In a second embodiment of the second aspect there is disclosed a VIGunit manufacture facility according to the previous embodiment of thesecond aspect, the evacuation head 8 further comprising a ceramicheating element 9.

In a third embodiment of the second aspect there is disclosed a VIG unitmanufacture facility according to any of the previous embodiments of thesecond aspect, wherein the ceramic heating element 9 is displaceable andconfigured to contact an evacuation tube tip 6 b and preferably pressthe tube tip 6 b to tip off the tube 6.

In a fourth embodiment of the second aspect there is disclosed a VIGunit manufacture facility according to any of the previous embodimentsof the second aspect, configured to perform the method according to anyof the first to fourteenth embodiments of the first aspect of thepresent disclosure.

In a first embodiment of a third aspect there is disclosed a vacuuminsulated glazing (VIG) unit comprising tempered glass panes 1,2comprising an evacuation cap 18 comprising an evacuation port 20 and asolder glass ring 19 arranged around the evacuation port 20, wherein theevacuation cap 18 is arranged on a pane face 1 a of a first or secondpane 1,2 and the evacuation cap 18 has a center distance substantiallyless than 25 mm from the pane 1,2 periphery, preferably less than 20 mm.

In a second embodiment of the third aspect there is disclosed a VIG unitaccording to the first embodiment of the third aspect, where theevacuation cap 18 is further situated at the corner of the pane face 1a, and the center distance hereby applies to both pane peripheries ofsaid corner.

In a second embodiment of the third aspect there is disclosed a VIG unitaccording to either the first or second embodiment of the third aspect,comprising a peripheral seal 3 and evacuation cap 18 seal 7 wherein bothseals 3,7 are adapted to be soldered at substantially the sametemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a VIG unit.

FIG. 2 shows a VIG unit and an evacuation head.

FIG. 3 shows a close up example of the evacuation head.

FIG. 4 shows another example of the evacuation head.

FIG. 5 shows temperature reading locations.

FIG. 6 shows chart of temperature differences and heating steps.

FIG. 7 shows a displaceable heater.

FIG. 8 illustrate the non-planar pane surface effects.

FIG. 9 illustrate alternative closures.

FIG. 10 illustrate alternative closures.

FIG. 11 show the temperature difference between surrounding air T1 andevacuation head T2.

DETAILED DESCRIPTION

FIG. 1 shows a vacuum insulating glazing (VIG) unit with 2 glass panes1,2. The VIG production method is done by providing a first and secondsubstantially parallel panes 1,2, a plurality of pillars 4 and aperipheral seal 3. The peripheral seal 3 is sealed for example by solderfrit or solder glass or metal solder. The panes 1,2 are spaced bypillars 4 which withstand the pressure when the VIG is evacuated and theatmosphere acts on the VIG. The pane 1 has an evacuation hole 5 with anevacuation tube 6. The evacuation tube 6 has a seal 7 for example solderglass or frit paste or metal solder. A part 6 a of the evacuation tubethereby remains enclosed in the evacuation hole 5 by the pane 1 and theseal 7, leaving an evacuation tube tip 6 b exposed to the atmosphere.

FIG. 2 shows a VIG now with an evacuation head 8 placed in contact withthe exterior face of pane 1. In a manufacture facility there may beseveral VIG units and evacuation heads 8 in one oven. The VIG productionmethod comprises heating the VIG in an oven to seal the peripheral seal3 and the tube seal 7. When the VIG cools in the oven the evacuating ofthe void V is started. Typically, at 150° C. or more, preferably at 300°C. or more. At 300° C. or more the seals 3,7 are still deformable andcan hereby better settle properly. The evacuating of the void V isperformed in a heating oven after substantially soldering the seal 3.The evacuation head 8 covers the evacuation hole 5 and associated tube 6and is adapted to evacuate the interior void V. After evacuation aheating element 9 melts the evacuation tube tip 6 b to seal the void V(known as the tip off step). The method of producing a VIG unit mayhereby be performed in an oven.

The evacuation head 8 performs best with a substantially hermeticcontact to the glass pane 1,2. This assumes the glass panes 1,2 areplanar.

The evacuation head 8 has a contact to the pane 1,2 having a diameter D.In the state of the art the diameter D is 50-100 mm. In the state of theart a large contact area (between glass pane and the evacuation head) isdesired so that the air molecules have difficulty passing i.e. longertravel to pass the hermetic contact area.

However, the evacuation of the VIG exposes the glass panes 1,2 to anatmospheric pressure pressing towards the void V (FIG. 1, Pa) and thismay warp the pane 1,2 surface as illustrated in FIG. 8a . Furthertempered glass is less planar than float glass due to the manufacturingprocess. In particular, tempered glass may have a curved periphery asillustrated in FIG. 8b . These factors work against the prior artevacuation head 8 and the hermetic contact to the pane face 1 a asillustrated in FIG. 8a,8b . And as explained later a large evacuationhead 8 also has adverse temperature distribution effects.

Consequently, it is advantageous that the contact width D is less than50 mm. Preferably the evacuation head 8 contact width D is below 45 mm.Most preferably the evacuation head 8 contact width D is between 24-40mm. In one aspect the width D is substantially circular and a diameterD.

With the specified size there is provided better evacuation and anenhanced VIG is produced. The pane non-planar face 1 a has bettercontact to a smaller evacuation head 8. This is advantageous withtempered glass and during evacuation inside a heated oven.

The evacuation head 8 with reduced width enables VIG units where theevacuation hole is located closer to the periphery. The evacuation hole5 or tube 6 has a center substantially less than 25 mm from the pane 1,2periphery, preferably less than 20 mm. In one example the evacuationhole 5 or tube 6 is further situated at the corner of the VIG and thecenter distance applies to both peripheries.

The pillars 4 are spaced by a distance S. Typically in the range of20-50 mm. With thick or strong glass panes 1,2 such as tempered glassthe distance S is about 40 mm. It is desired to increase the distance Sdue to appearance and better thermal insulation. In one aspect theevacuation head 8 contact width D is equal or smaller than the pillar 4spacing distance S. Hereby an enhanced evacuation and VIG is provided.

Reducing the contact width D has challenges, because the evacuation head8 needs to accommodate a heating element 9 and it needs a chamber 10 toaccommodate the evacuation tube 6. Further the evacuation head 8 mayhave at least one surrounding conduit 13 (for vacuum suction to fix theevacuation head 8 to the pane) which also requires room and evacuationtubes 11, 12 to different vacuum pumps. Optionally also a seal, O-ringor gasket towards the glass contact surface (not shown). Optionally also(FIG. 4), a shield plate 15 placed in the chamber 10 so that the tubetip 6 b is exposed to the heat in the chamber 10 and the remaining VIGis not affected by the heat.

Manufacture of VIG units is quite temperature dependent. The peripheralseal 3, the glass pane 1,2 structure and treatments, the evacuation holeseal 7 and the degassing of materials all depend on the temperature.Through the steps of producing a VIG the temperature is varied (FIG. 6.shows three different steps) to degas the void V and solder the seals 3.In case the evacuation head 8 is used to tip off (i.e. seal off) theevacuation tube tip 6 b there is a heating element 9 in the evacuationhead which shortly heats to for example 700-1200° C. degrees to melt thetip of the evacuation tube 6.

In particular, when using tempered glass, it is particularly desirableto keep the temperature of the tempered glass below the annealingtemperature of the tempered glass, which otherwise will lead to loss oftemper and reduced glass strength. Accordingly, a method of producing aVIG unit according to the disclosure, and wherein the VIG bodyproduction in an oven includes heating the VIG unit in the oven, maycomprise in all steps keeping the temperature below an annealingtemperature, which detrimentally affects the tempered glass, such askeeping the temperature below 400° C., which is a common annealingtemperature for many tempered glasses. As, in some embodiments of thepresent disclosure, the evacuating of the void V is done at 150° C. ormore, preferably at 300° C. or more, it is preferable that thetemperature of the oven is between 150° C. and 400° C., preferablybetween 300° C. and 400° C. during evacuation.

In the state of the art the heater element is typically a fixed tungstencoil heater. The prior art tungsten coil has the drawback, that it canproduce metal deposits on the glass and it is less durable and producesa varied seal of the tube tip 6 b. Further, the prior art evacuationhead comprising a tungsten coil has the drawback, that the tungsten coilcan only be operated under sufficient vacuum, which prevents heatingwith a tungsten coil under atmospheric pressures.

The evacuation head 8 has a heating element 9. The heating element 9 maybe a ceramic heater. The ceramic heating element 9 may comprise a heatgenerating resistor component. The ceramic heater may comprise apiezoresistive component. The ceramic heater may comprise anelectrically resistive ceramic component.

The ceramic heater 9 can be located within the evacuation head 8. Thepower cables can for example be provided inside the evacuation tubes11,12 and/or by the evacuation tubes 11,12 if they have sufficientelectric conductivity. Hereby the hermetic properties of the evacuationhead 8 are not affected by the h 9.

A ceramic heating element 9 is more durable and provides reliable VIGproduction. A ceramic heater 9 has a more constant heat profile. Theheating element 9 in the prior art shortly raises the local temperatureto melt the tip 6 b of the evacuation tube 6. But, as explained below, aceramic heating element 9 also enables heating to multiple temperatures.

As the majority of the heat transfer under vacuum is by heat radiation,particularly suitable sources of ceramic heaters are such ceramicheaters that emit most strongly within the IR-absorptive region ofglass, in particular silicon nitride and/or aluminum nitride ceramicheaters. Such ceramic heaters have particularly strong emission in thefrequency band from 4 to 13 μm, making them particularly suitable in theVIG manufacture.

In some embodiments, the ceramic heating element 9 may be a cylinder asdepicted in the figures of the present disclosure. Where homogenoussurface radiation is preferred, the ceramic heater can be flat discshaped, or where focused radiation is desired, e.g. for better tip offof the evacuation tube tip 6 b, parabolic shapes would be preferred. Afurther advantage of the use of ceramic heaters is the possibility tocombine two or more differently shaped heaters to obtain a variety ofradiation profiles based on the combined shaped heater. E.g. a flat discshaped heater can be combined with an elongated cylinder shaped heaterto provide both focused and planer energy to the surface. Further, byhaving separate energy supplies, the two or further heaters can beoperated separately, depending on the design needs of the VIGmanufacture.

The VIG manufacture is enhanced when the temperature throughout the VIGbody is continuous i.e. minimize the temperature differences across thebody. When the evacuation head 8 is placed on the pane face 1 a of thepane it affects the local temperature. FIG. 5 shows different locationsfor established temperature T2 inside the evacuation head 8. TemperatureT1 in the surrounding air. And temperature T3 in the junction betweenthe panes 1,2. FIG. 6 shows a chart of the difference or delay intemperature during the VIG manufacture heating steps. It shows that thepane 1 glass temperature gradient is different at the location of theevacuation head 8. The local temperature T2 at the evacuation head 8 islower.

It is advantageous to ensure the temperature under the evacuation head 8matches the surrounding VIG body temperature (i.e. close to T3),respectively surrounding air temperature T1. Even a 10-30° C.temperature difference can adversely affect the VIG manufacture. To thisaim, the evacuation head 8 can be equipped with a temperature sensor(not shown) to continuously measure the temperature difference exteriorand interior to the evacuation head. A closed loop current feedback tothe heating element 9 would then be advantageously employed.

In particular, where the solder glass is a low temperature solder glass,in particular a lead-free low temperature solder glass, such as aVBZ-solder glass, it may be desirable to compensate for the temperaturedifference between VIG body temperature, respectively surrounding airtemperature T1, and the temperature T2 under the evacuation head 8, asthe narrow windows of temperatures applied leave little room fordeviations if a sufficient solder glass is to be created by thesoldering process. E.g. tempered glass is negatively influenced by hightemperatures and long heating times, hence incomplete matching of thetemperature T2 under the evacuation head 8 to the solder temperature,will lead to longer soldering times and hence to increased loss oftemper in the glass.

In one aspect, the evacuating head 8 has fins to enhance the thermaltransfer between the surrounding air and the evacuation head 8. Herebythe temperature under the evacuation head 8 T2 has a better match to thesurrounding temperature T1.

A further advantage of matching the temperature T2 under the evacuationhead 8 to the temperature of the surrounding air T1 lies in securingadequate parture of the solvents and binders comprised in the solderglasses used for manufacturing the VIG units of the disclosure. If thetemperatures under the evacuation head 8 is too low, reduced parture ofsolvents and binders will be observed, resulting in incomplete solderingof the solder glasses at a later stage or increased loss of temper dueto increased soldering times.

In one aspect the heater 9 has a first heating temperature and a secondheating temperature. The second heating temperature is nearly twice ashigh as the first heating temperature. The first heating temperature isthe peripheral seal 3 solder temperature (for example 300-450° C.), andthe second heating temperature is the sealing temperature of the tubetip 6 b (for example in the interval of 700-1200° C.)

In one aspect, when the heater is a ceramic heater, the heating element9 is on at least for 15 minutes for the first temperature. The heatingelement 9 substantially heats for the duration of at least one heatstep, preferably the solder step. The state of the art, tungsten heatersare usually on for seconds only.

The first temperature provides a substantially uniform VIG bodytemperature T2 beneath the evacuation head 8. Hereby the temperatureunder the evacuation head 8 has a better match to the surroundingtemperature T1. This provides a better tube seal 7 solder and theremaining VIG is not affected by heat gradients and stress.

In another aspect (FIG. 4) the evacuation head 8 first and secondtemperature is provided by a first heating element 9 and a secondheating element 14. The second heater may be outside the chamber 10.Hereby each heater is customized to heat to the specified first andsecond temperature.

FIG. 7 shows an evacuation head 8 with the ceramic heating element 9.Here the ceramic heating element 9 is displaceable and configured tomove towards the tube tip 6 b and contact the tube tip 6 b. The ceramicheating element 9 is heated to the tip off temperature such as of700-1200° C. and brought into contact with the tube tip 6 b. The tubetip 6 b may be pressed by the ceramic heating element 9 and deformedduring the seal off. Hereby the sealing of the tube tip 6 b is reliableand has little influence on the remaining VIG body. The displaceableheater 9 may be employed in an oven during the VIG sealing andevacuation and tip off.

The ceramic heating element 9 displacement may for example be in theinterval of 1-3 mm. An actuator 16 may displace the ceramic heater 9.The actuator 16 may be based on a material which expands when heated tothe tip off temperature. The actuator may be an electric piezo actuator.The actuator 16 may operate by way of an electromagnet 17 such as anexternal electromagnet 17, which displaces the heating element 9. Theseexamples of actuators ensure the hermetic properties of the evacuationhead 8 are intact while providing operation in the hot oven environment.Other actuators may be employed.

Above, the present disclosure has been exemplified using an evacuationtube 6 inserted into evacuation hole 5 and soldered to the pane face 1 aof the first pane 1. The present disclosure, however, is not limited inthe manner in which evacuation occurs, nor in the art or construction ofthe evacuation tube 6.

In the art (c.f. e.g. US 2009/0155500 A1, US 2012/0148795 A1, bothherein incorporated by reference) many other evacuation solutions areknown for use with an all-metal cup of the prior art. The advanced intechnology as described herein regarding the construction and design ofevacuation heads 8 allow for improved implementation of these furtheradvantageous implementations of the evacuation tube 6.

One common method of closing an evacuation hole 5 is by allowing solderglass (in the form of a solder glass or frit ring, cf. e.g. FIG. 5 of US2012/0148795 A1) to melt down into the evacuation hole 5, thusdispensing with the evacuation tube 6. This prior art method isadvantageous in that it requires lower melting temperatures than what issufficient for melting the glass of the evacuation tube. However,disadvantageously, it requires significantly longer melt times. With thetungsten heater, as employed in the prior art, and in particular withthe large evacuation heads of the prior art, this has been observed toresult in damage to the pane 1, e.g. by the aforementioned deposit fromthe heater to the surface. By reducing the evacuation head diameter D asdetailed herein and/or by using a ceramic heating element 9 forlocalized heating, improved melting with shorter on-times can beachieved and concomitantly reduced damage to the pane 1. In the samemanner, bung-like closures or cap-like closures can improved be solderedto the pane face 1 a with less damage using the evacuation heads 8detailed herein.

FIG. 9 details elements of the further improvements, which will bedescribed below. In FIG. 9a , a disc shaped evacuation cap 18 has beensoldered to the pane face 1 a of the first pane 1. Preferably, theevacuation cap 18 is partly inserted into the evacuation hole 5. The cap18 comprises an evacuation port 20 and a solder glass ring 19 arrangedaround the evacuation port 20 on the cap 18, the solder glass ring 19facing away from the interior void V, when the cap 18 is inserted intothe evacuation hole 5. Preferably, the cap 18 has a depression forcomprising the solder glass ring 19 and the evacuation port 20. FIG. 9bshows the situation after evacuation of the void V and subsequentclosure of the evacuation port 20 by melting the solder glass ring 19,which under the influence of gravity, will flow into the evacuation port20 thereby forming a tight seal for the evacuated void. For improvedheat transfer and protection of the evacuated void V as well as theglass pane 1, the evacuation cap 18 is manufactured from metal, althoughglasses are suitable as well.

Such evacuation caps 18 are particularly preferable in VIG manufactureas they do not, contrary to the evacuation tubes 6, require furthercapping to protect the sealed tube from external damage, hence savingmanufacturing steps and cost without loss of VIG life time in use.However, their use has hitherto been limited by the fact that with theprior art evacuation heads, unwanted heating of either or both of pane 1and cap 18 would lead to thermal expansion of these elements and crackformation where pane 1 and cap 18 interact. The present, localizedheating obtainable by the evacuation heads of the present disclosure,overcome these problems.

Also suitable for use with the evacuation head 8 of the disclosure is adisc shaped evacuation cap 21 as depicted in FIGS. 10a and 10b , whereinthe solder glass ring 19 and the evacuation port 20 are no longerlocated on the top of the evacuation cap 21, but rather at its peripheryand in between evacuation cap 21 and glass pane 1. Here, the disc shapedevacuation cap 21 is prepositioned in the evacuation hole 5 and providedwith a discontinuous and/or dented solder 22 between the evacuation cap21 and the glass pane 1, wherein the spaces and/or dents 23 between thediscontinuous or indented solder 22 serve the function of the evacuationport 20 of the previous embodiment. When the ceramic heater 9subsequently heats the solder to form the solder glass, the spacesand/or dents 23 between the discontinuous and/or dented solder 22coalesce into a continuous solder glass in response to the heating. Thisevacuation cap is particularly suitable for use with a flat, disc shapedceramic heating element 9, having the added benefit that the distancebetween heater and evacuation cap can be reduced to within 0.5 mm to 2mm for improved heat transfer between heater and evacuation cap.

Now some effects are described in particular with reference to FIG. 11,wherein is shown the experimentally measured surrounding air temperatureT1 and the temperature T2 under the evacuation head 8 over 45 minutes.The solder seal 7 for the evacuation tube 6 is temperature sensitivebecause the seal 7 requires enough heat to seal properly (for example300-450° C.) and the reduced temperature beneath the evacuation head 8as explained in FIGS. 5 and 6 may prevent a proper seal. This is solvedby the heating elements 9,14 and/or evacuation head 8 as presented inthis disclosure. The disclosed evacuation head 8 provides more uniformtemperature because it covers less area. And the heating element 9 andoptionally heating element 14 provide a temperature at the evacuationhead 8 which matches the surrounding oven sealing temperature.

The ceramic heater enables a compact evacuation head with enhancedhermetic contact and enhanced thermal distribution below the evacuationhead.

Further, the solder seal 7 for the evacuation tube 6 is temperaturesensitive because the tube tip off heat (700-1200° C.) may deterioratethe seal 7 and may weaken a tempered glass pane or coated pane. Thisdrawback may be solved by the shield plate 15 (FIG. 4) or by a ceramicheater 9 as disclosed (which may also be displaceable as explained).

Generally, the disclosed embodiment of the ceramic heating element 9 andthe disclosed embodiment of the displaceable heater 9 and the disclosedembodiment of the evacuation head 8 with a defined size D are suitablefor combination, but likewise the three embodiments may also be employedseparately.

Generally, the present disclosure is suitable and advantageous for atempered glass VIG.

Generally, the evacuation head 8 and/or ceramic heater 9 may be employedoutside an oven.

Although the present disclosure has been described in detail for purposeof illustration, it is understood that such detail is solely for thatpurpose, and variations and combinations can be made therein by thoseskilled in the art without departing from the scope of the appendedclaims. The temperatures indicated are not limiting unless statedotherwise.

The invention claimed is:
 1. A method of producing a vacuum insulatedglazing (VIG) unit, the method comprising: providing first and secondsubstantially parallel glass panes, a plurality of pillars, and aperipheral seal between the first and second glass panes; providing anevacuation hole for evacuating a void through the evacuation hole to apressure less than atmospheric pressure, wherein the first and secondglass panes are tempered glass; covering the evacuation hole with anevacuation head, wherein the evacuation head is configured to have asubstantially hermetic contact to a surface of the first glass pane,wherein a distance between pillars of the plurality of pillars is 38 to42 mm; wherein a contact width of the evacuation head to the surface ofthe first glass pane is equal to or less than the distance between thepillars of the plurality of pillars; and evacuating the void through theevacuation head.
 2. The method of producing the VIG unit according toclaim 1, wherein the evacuation head is configured to reduce atemperature difference between a temperature of a VIG body beneath theevacuation head and a temperature surrounding the VIG body.
 3. Themethod of producing the VIG unit according to claim 1, furthercomprising evacuating the void while the VIG unit is disposed in anoven.
 4. The method of producing the VIG unit according to claim 3,further comprising heating the VIG unit in the oven, wherein the heatingis at a temperature less than an annealing temperature of the temperedglass.
 5. The method of producing the VIG unit according to claim 3,wherein the evacuating of the void is at a temperature of 150° C. orgreater.
 6. The method of producing the VIG unit according to claim 3,wherein the temperature of the oven is between 150° C. and 400° C. 7.The method of producing the VIG unit according to claim 3, wherein theevacuating of the void is performed in the oven after substantiallysoldering the peripheral seal.
 8. The method of producing the VIG unitaccording to claim 3, further comprising substantially soldering theperipheral seal in the oven, and subsequently evacuating of the void. 9.The method of producing the VIG unit according to claim 3, furthercomprising sealing an evacuation tube tip of an evacuation tube byheating, wherein the heating is provided by a heat element in theevacuation head.
 10. The method of producing the VIG unit according toclaim 1, wherein the evacuation head has a substantially circular shapeand the contact width is a diameter of the substantially circular shape.11. The method of producing the VIG unit according to claim 9, whereinthe evacuation head further comprises a ceramic heating element, andwherein the method further comprises heating the ceramic heating elementand sealing the evacuation tube tip of the evacuation tube.
 12. Themethod of producing the VIG unit according to claim 11, furthercomprising: heating the ceramic heating element to a first temperatureto provide a substantially uniform VIG body temperature T2 beneath theevacuation head; and heating the ceramic heating element to a secondtemperature to seal the evacuation tube tip.
 13. The method of producingthe VIG unit according to claim 9, wherein the evacuation tube is anevacuation cap comprising an evacuation port and a solder glass ringarranged around the evacuation port.
 14. The method of producing the VIGunit according to claim 1, wherein the contact width of the evacuationhead to the surface of the first glass pane is 24 mm to 40 mm.